Gary Z

A while back I was discussing my car with a local tuner and I mentioned that I routinely trap above 7000 rpm. He said "no way" given that I have stock LS1 lifters and beehive springs. He said hundreds of hours of LSx dyno experience convinced him that it was impossible without severe valve float. My forged 347 has stock 243 heads with LS6 valves and PAC 1518 springs. I deliberately selected a cam that wouldn't require dual valve springs but at the time I didn't expect to spin above 7k. Only later I decided to spray. Now I'm near 130 mph with 4.33 gears and 26-inch tires. I detect no power loss at 7100 rpm. I doubt that my valves are floating. What say y'all. Oh yeah - stock pushrods too.

nostixs

my only concern would be if the rockers are 100% stock without the comp needle bearing upgrade, is that a needle bearing come out and destroy your motor. The factory bearings are not caged and are notorious about this. Also i am not familiar with the rpm range of the ls6 valve springs. Maybe be a good time for some valvetrain upgrades ....it would be cheap insurance. Hope this helps.

LS1-450

iTrader: (33)

The valves are floating.

vettenuts

iTrader: (4)

You would have to verify on a dyno but with LS6 valves, PAC 1518's and stock rockers, I can believe it will go to 7K RPM.

Gary Z

They may be. I just don't see any evidence of float. For example, the attached log.

z28241

iTrader: (13)

Why would u gamble on this?!, Dual Valve springs are good insurance!!! Espicially for 7 g revs ..Common Sense..Beehives wont last over and over bro..

Gary Z

A combination of curiosity and stupidity. I first went above 7k by accident – I logged 7800 rpm after a WOT 2-1 shift. I pulled the valve covers and did a compression test and everything seemed ok – no broken springs or bent valves. The motor still made good power. After I started spraying I saw tens were within reach so I’ve just been pressing my luck. My fuel cutoff is at 7200. My window switch upper limit is at 7100. Also, I like the beehive spring. I think it is a brilliant development. Dual springs seem less elegant. I think the the lightweight LS6 valves are a significant help.

printmanjackson

iTrader: (1)

I bet you got pistons marking the valves if you pull the heads


good luck

Gary Z

Maybe but I don't think so. My pistons do have -2 cc valve reliefs.

Gary Z

Thanks, Vettenuts. I know you are a serious student of valvetrain dynamics.

LS1-450

iTrader: (33)

Evidence is piston knick, valve edge knick, bent valve, valve guide wear, valve stem wear, valve seat evidence, uneven wear where valve mates w/ valve seat. Maybe even a broken spring or valve tip or rocker tip marks or excessive wear.

chevynation

iTrader: (8)

I was with you until you said "stock pushrods"...

2fresh

iTrader: (20)

troll detected? with the stock push rods comment

Gary Z

Thanks. I have looked under the valve covers. I'll pull the heads and have a closer look in November at the end of drag season. But at some point valve float must cause power loss. Can there be the sort of valvetrain damage you mention from very short duration float?

Gary Z

Since I have lighter valves and lower spring pressures (compared to duals) I decided I didn't need extra beefy pushrods. And stock pushrods are not as weak as some think. Cut one in half sometime, I bet you'll be impressed by the wall thickness. When I built my engine I had some name-brand chromoly pushrods. They looked crude compared to the very high quality stockers. I prefer the perfect little ball to a formed end. The stockers were the length I needed so I went with GM.

David_viny

I could see this. The LS7 can rev to 7,000rpm stock (7,100 fuel cut actually), and you have a lighter valvetrain and stronger springs then an LS7.

vettenuts

iTrader: (4)

This is actually where more stability can be gained. Thicker wall will buy you a little bit, but larger OD will buy you a lot. If you pull the heads over the winter, I think with the RPM you are turning that larger pushrods could help. Here is a link to some investigation that I did for my motor. Here is the link: Link

As an update, I returned to the dyno this spring and did find that from 6,100 RPM up to fuel cutoff that I picked up a few HP but more importantly the curve didn't drop off as quickly as it did with the 5/16" pushrods. My original dyno with the new pushrods was indeed lower due to the winter fuel. When I returned, I made sure the summer fuel was in the gas stations. The HP was not the important part of this experiment, it was the valve train stability that will help keep things under control and extend the life of the motor.

Steve Gunn

Seems like a 28" tire might be cheaper than what "could happen". More power to ya, though. You're bangin' hookers without a condom, my friend! (While running with scissors)

LS1-450

iTrader: (33)

If there is float, you will see some evidence in wear to the related parts regardless of duration.

Additionally, if you want to check using logged info, logging the engine is a more accurate place to look than the rear wheels (RWHP, RWTQ). Further, don't spray while testing. It can partially mask the issue. Make a run without nitrous & log MAF & MAP. Even A/F ratio can be slightly tainted by the valve float unless it's already been accounted for while tuning RWHP. Anyway, logging MAF & MAP during WOT will indicate valve float more accurately than RWHP logs do.

Gary Z

Thanks for the suggestions. I datalog all my dragstrip passes - I have bushels of data. I’ve never seen any suspicious anomolies in my MAP data but now that you mention it it makes sense that valve float could show up there. The MAP signal is always much cleaner (less noisey) than unfiltered MAF data so I assume smaller effects would be more visible in the MAP data. I went back and plotted MAP data from the run above. I also have data from a motor pass the same day although then I was only above 7k at launch.

I may have caused some confusion labeling "Vehicle Speed" as "Rear Wheel Speed". I do that to account for wheelspin. The parameter is VSS.